The present invention relates generally to measurement of time delays between an events and a response to the event. In particular, the present invention relates to the detection of the response of a system to an initiating event.
Throughout industry, processes depend on a sequence of events where one action is taken in response to an initiating event: a tank fills, a valve closes once the tank fills, an agitator begins to agitate when the tank valve is closed. Sometimes the action is in response to an unexpected event that has safety consequences. For example, at a nuclear power plant, if a control rod drops into the nuclear core by accident, it may adversely affect the power distribution in other areas of the core. The response might include notification of the operator and a check on the power to the control rod actuator, for example.
Especially under circumstances where a response needs to occur within a short time after an initiating event for safety reasons, it is important to know that a response will in fact occur and will occur within a prescribed time. Because it is important, these systems may be audited to see if they respond as they are designed to do. Their response time is measured against a simulated initiating event and compared to the specified response time.
At nuclear power plants, some responses must take place very quickly after initiating events in order to prevent damage to equipment or perhaps the release of radioactive material. Measuring short time intervals to verify that response times are within specifications is a significant problem.
See for example, the patents issued to Palusamy et al., U.S. Pat. No. 4,908,775; Miller et al., U.S. Pat. No. 4,752,869; Sawyer et al., U.S. Pat. No. 4,640,812; and Dennis et al., U.S. Pat. No. 4,517,154, for examples of patents that relate generally to measurement of responses of systems at nuclear power plants.
Nonetheless there remains a need for a simple system that will measure when a response occurs following an initiating event, particularly, when the response is the lighting of a warning light to alert an operator that an initiating event has occurred.
The invention is an apparatus for determining the interval of time between an initiating event and a visual response to that event. Typically, the present apparatus is useful when verifying that short and consistent intervals are being obtained between the initiating event and response events, such as in the response system at nuclear power plants. These systems are to be tested periodically to see if the response times are within specification. The present invention makes testing much easier and more accurate.
In a preferred embodiment, the present apparatus includes an optical sensor mounted in close proximity to a warning light and connected electrically to electrical circuitry that processes the electrical output of the sensor so that an analog signal results. The analog signal can be forwarded to an output device to display changes in the signal that result from changes in the intensity of the warning light, i.e., the light has gone on or off. If the signal that caused the warning light to go on is simultaneously sent to the same output device, then a comparison of the times when the two signals (initiating and response) are received reveals the response time.
An important feature of the present invention is that the sensor can be mounted easily near the warning signal light. No electrical connection need be made with the light and its distance from the warning light need only be such that a direct exposure is available and the interference from other sources of light be relatively less than the visual signal from the warning light.
Another important feature of the present invention is the use of an optical signal from the optical sensor. Use of an optical signal avoids the need to calibrate the signal to determine on and off intensities of different lamps and different levels of ambient light.
Still another feature of the invention is the use of an optical sensor rather than other types where the signal speed between the warning lamp and sensor might be significant with respect to the response time. With optical sensors, the signal speed is virtually instantaneous.
Other features and their advantages will be apparent to those skilled in the art of instrumentation from a careful reading of the Detailed Description of Preferred Embodiment, accompanied by the following drawings.